Does anyone know the answer to this?

A surgeon says to a tramp 'ill give you 200 pounds if i can cut off your left arm?' the tramp agrees so the surgeon wraps up the tramps arm and sends it off to a man, this man is satisfied with the arm so he wraps it back up and sends it to another man, this man is also satisfied with the arm so he wraps it back up and sends it to the another man, this man is satisfied with the arm and throws it in the bin.....WHY???